Typical parallel hybrid electric vehicles include an internal combustion engine, an electric motor, and a battery. Parallel hybrid electric vehicles typically operate using the electric motor and/or the internal combustion engine as prime movers to propel the vehicle. That is, the vehicle wheels may be rotated using only the electric motor, only the engine, or using some combination of torque from both prime movers. Generally, the vehicle may be operated at low speeds with the electric motor only, and during periods of high acceleration and/or high vehicle speeds with a combination of both the engine and the motor. Typically, the engine and/or a regenerative brake may be used to recharge the battery, and the battery may be used to rotate the motor.
When the engine is used to recharge the battery, the motor may be used to propel the vehicle during the electric only operation. Further, the engine may propel the vehicle during engine only operation while rotating the motor (as a generator) to recharge the battery. A hybrid electric system will typically maintain the state of charge of the battery within a prescribed range. That is, the battery may be used to power the motor to propel the vehicle with the engine not operating for extended periods while the battery state of charge is within, for example, between forty percent (40%) and eighty percent (80%) of maximum charge. A controller for a hybrid electric vehicle may automatically initiate charging of the battery when the state of charge falls below fifty percent (50%) of maximum charge during vehicle operation. Many hybrid electric vehicles operate the engine, motor and battery while targeting a desired state of charge value for the battery. That is, if the state of charge (expressed as a percentage of maximum) falls below the desired value (or range), the battery will be charged, and if the state of charge exceeds the desired value (or range), the battery will be discharged, usually by providing torque to propel the vehicle.
Generally, the operator may not know when the vehicle will switch from the electric only operation to operations using the engine, and the operator cannot control the amount of charge (state of charge) of the battery, as the vehicle will typically maintain the state of charge automatically. Further, the operator will not know the range available for operating without the engine propelling the vehicle.
Many regenerative brakes operate as a mechanism that reduces vehicle speed by converting some of the vehicle's kinetic energy into another useful form of energy. This captured energy may be then stored for future use, such as in the battery, or fed back into other vehicle components, such as is disclosed in commonly owned U.S. Pat. Nos. 4,246,988; 4,986,383; and 7,076,946. The regenerative brake may use the motor as a generator to convert kinetic energy to electricity, or other components may be used to generate electricity.
While many parallel hybrid electric vehicles include numerous controls, an operator may not be able to control the operation of the engine, or the battery state of charge before or during electric only operation. Further, an operator may not know when the engine will start during electric only operation.